Signatures of the Tricritical Point in QCD

Abstract

Several approaches to QCD with two massless quarks at finite temperature $T$ and baryon chemical potential $\ensuremath{\mu}$ suggest the existence of a tricritical point on the boundary of the phase with spontaneously broken chiral symmetry. In QCD with massive quarks there is then a critical point at the end of a first order transition line. We discuss possible experimental signatures of this point, which provide information about its location and properties. We propose a combination of event-by-event observables, including suppressed fluctuations in $T$ and $\ensuremath{\mu}$ and, simultaneously, enhanced fluctuations in the multiplicity of soft pions.